MACDOUGAI^ACTION OF LIPOIDS IN GROWTH. 



43 



The above applies to cells filled with water and immersed in water. 

 When the contents include substances already in solution, such as the 

 salts of potassium and sodium, the action of these salts on the colloids 

 both as to their solution and hydration are to be taken into account. 

 As hydroxide at o.oiM potassium is found to retard the hydration 

 of agar more than sodium. Whether this would be true of the desig- 

 nated colloidal mixture, and as a chloride, has not been tested, but 

 probably this action would be reversed.^^ 



The ionic velocity and speed of penetration of the potassium would 

 be greater, and its superior osmotic action would result in a greater 

 endosmosis than in the cell containing sodium. 



That solution of colloids, the penetration of the pores by colloidal 

 matter, and the action of salts and other compounds act progressively 

 may well be inferred from the long-continued swelling action of these 

 biocolloids in dilute salt solutions and amino-compounds, on the one 

 hand, and on the other by the fact that when biocolloidal cells are set 

 in action the rate of endosmosis rises until some time in the third 

 24-hour period, no change having been made in the preparation mean- 

 while. A decline in the rate takes place during the fourth day, but 

 the decrease is so slow that endosmosis may continue for 60 to 80 

 days. Such action is illustrated by the following figures : 



The above procedure, it should be noted, is one that characterizes 

 the agar-gelatine-soap biocolloid and is not shown by agar in which 

 endosmosis falls off rapidly. 



The foregoing tests serve to illustrate the operation of the arti- 

 ficial cell which it was proposed to use in determining the possible 

 action of a peripheral layer of lecithin or lipoids in the absorption of 

 salts by the plasmatic layer. Lecithin had been incorporated with 



